This one’s a little tough to spot at first, but if you click to expand this photo, you’ll see the telltale blue smoke of a gasoline-and-oil-burning two-stroke Peugeot moped on Valencia Street in the Sunny Mission district.

Depending on the state of tune, you can have something like half the fuel and oil you put in spewed out the tailpipe unburned. Tuk tuk tuk tuk tuk tuk….

Such are the ways of aging two-stroke engines. But fashion has a price, after all.